The present invention relates to a control plate as it is for instance used in pneumatic or hydraulic controls. An example of such a control plate is a transmission control plate with which automatic transmissions are controlled hydraulically.
Control plates often comprise a metallic layer, which comprises passage openings for the hydraulic fluid, e.g. oil. This layer—often also referred to as distance layer or carrier layer—typically has a thickness of about 1 mm or more. Adjacent to this metallic layer, valve housings are arranged by means of which the flow of the hydraulic fluid is controlled.
In order to fulfil its control purpose, the hydraulic fluid flows in channels on surfaces of the respective parts of the transmission which are covered by the transmission plate. The transmission plate comprises a plurality of passage holes through which the hydraulic fluid can pass from one surface to the opposite one and continues to flow in another channel. Dependent on the operational state of the transmission, the hydraulic fluid flows with different velocities and pressures in different channels. Also dependent on the operational state, it shows no movement in some of the channels. As a consequence, these channels need to be sealed against each other, although the same hydraulic fluid is present in all of them. Further, the metallic layer needs to be sealed against the outside at its outer edge. Therefore, the oil passage openings individually or in groups, isolated or continuously with the channels opening to the respective oil passage openings need to be encircled by a sealing line which considers the pressure conditions in the hydraulic oil. Further, a sealing of the outer edge of the control plate, is required, too.
To this end, according to the state of the art, a coating is applied to the metallic layer at least in sections surrounding the openings, for example using screen printing. This coating shows an essentially uniform thickness. It consists of an elastomer which is compressed between the metallic layer and the adjacent part when the layer is compressed with the adjacent part during tightening of the screws and this ways provides for its sealing effect.
Such a partially coated layer is however related to the problem that the screw forces are introduced locally in the area of the screw holes, so that in the area around the screw holes high compression forces are present while in the areas in between the screw holes the compression forces are considerably smaller. This results in an imbalanced sealing effect of the coating. Moreover, there are situations where the compression must not be the same over the complete extension of the metallic layer, but in particular areas, a deliberately increased or reduced compression may be required.
In order to solve this problem, in the state of the art, additional active gasket layers are arranged next to the metallic layer—the distance layer. These gasket layers comprise additional sealing elements, e.g. embossed beads, which in particular extend around the oil-carrying passages to be sealed. Such sealing beads contribute additional compression forces to the regions around the areas to be sealed. In a similar manner, DE 10 2007 040 101 A1 proposes to provide for a step in the distance layer, which step surrounds the areas to be sealed. This leads to an increase of the compression in the area of the step and causes an improved sealing around a region to be sealed, such as an oil passage.
It is disadvantageous with these solutions that they either require additional layers or an additional forming of the distance layer for the improvement of the sealing effect.